This is a semantic question, I would like to know if you have clarification on rule of intention. In the prerequisites it states you cannot have any levels in any other class, however nothing prevents you from multiclassing until the 3rd feat in the related feat chain. The question comes to this, if you multiclass after your 4 levels in fighter for example and take the fighter feat, but decided you would like to take levels in cleric. Do you no longer meet the prerequisites for the feat and therefore lose said feats benefits?
Edit I wanted to clarify why I am asking, only because Adventurers guide pg. 380 states:
"You must meet any prerequisite specified in a feat to take that feat. If you ever lose a feat's prerequisite, you can't use that feat until you regain the prerequisite. For example, the Grappler feat requires you to have a Strength of 13 or higher. If your Strength is reduced below 13 somehow — perhaps by a withering curse — you can't benefit from the Grappler feat until your Strength is restored."
I just wanted to know if this was the original intention of these feats or if the 3rd feat was so posed to be the full restriction.